


Tiger's Cave, Tiger's Cub

by hearthope



Category: Haikyuu!!
Genre: Alternate Universe - Modern with Magic, Doctor Yaku, Enemies to Friends to Lovers, M/M, Police Officer Kuroo, but like they're not really enemies they're just. kuroyaku. you know
Language: English
Status: Completed
Published: 2018-12-26
Updated: 2018-12-26
Packaged: 2019-09-27 19:33:36
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 11,776
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17168042
Author URL: https://archiveofourown.org/users/hearthope/pseuds/hearthope
Summary: Tetsurou calls it something akin to friendship.  Kai calls it sweet.  Kenma calls it the tiger’s cub.Great suffering leads to great results, Kuroo knows.  He's just not yet sure what sort of great results can come from being stuck on a case with Yaku as his key resource.





	Tiger's Cave, Tiger's Cub

**Author's Note:**

  * For [priin](https://archiveofourown.org/users/priin/gifts).



> riin!!! merry merry merry christmas!!!! this is a touch late, i'm so sorry, i didn't get a chance to post this when i wanted, but !!!!! i hope you like this all the same!!!!  
> i tried to keep a touch of magic to this, and to keep it sweeter than anything. i hope you love it!^^ ♡

**虎穴に入らずんば虎子を得ず**

_If you do not enter the tiger’s cave, you will not catch its cub._

 

* * *

 

Tetsurou might not be the medical expert, and his mind might be a little bit hazy from the blood loss and whatever medication they injected him with, but he’s nearly positive there’s absolutely no reason for Yaku to be pressing _this_ hard on him. Pressure’s important, he knows, he’s read enough journals and had Yaku lecture him enough times about it, but there’s gotta be a limit. There’s definitely a limit. Tetsurou’s almost positive.

 

“You’re going to break a rib,” he chokes out, a little breathless. “Are you trying to kill me?”

 

“Clearly, whoever tried to didn’t do it right,” Yaku mutters. “I’m doing them a favor by finishing the job.”

 

“I should sue for malpractice. Get your medical license rev— _ah!_ “ Tetsurou flinches as Yaku’s hand moves over the wound in his side and pulls out whatever fragmented bits he’s finally pulled to the surface. “You really are trying to kill me. Oh my god.”

 

Yaku rolls his eyes and wipes a damp cloth over Tetsurou’s skin. “You’re overdramatic.”

 

“Tell Kenma I love him. Leave my stash of Kit-Kats to anyone but Lev.” Unwilling tears prick at Tetsurou’s eyes. He’s always had the world’s lowest pain tolerance. It should, in theory, make him more cautious, less prone to visits to Yaku’s office. Instead, this is his third visit in less than four weeks.

 

“I really am going to finish the job,” Yaku huffs. “You’re such a baby.”

 

“And you could stand to be more gentle! Where’s the bedside manner?” He grips the railing at the edge of the cot he’s lying on. Kenma abandoned him, going off for a shower or to get food or maybe just to sleep under Yamamoto’s desk. All viable options. Either way, he’s got no hand to hold. “You’re never this rough with Kenma.”

 

“Kenma doesn’t get shanked on a weekly basis. Are you going to shut up any time soon? Stop distracting me from doing my job?”

 

Tetsurou scrunches his nose and looks away. Maybe it’s a good thing Kenma’s not around. He’d be the first to call out the childish pettiness.

 

Yaku focuses back in on Tetsurou’s wound, which is bleeding significantly less now. Loathe as he is to admit it, Yaku _is_ good at his job, and will have Tetsurou sealed and back on his feet in no time.

 

Tetsurou braves a glance at where Yaku’s waving a hand over the cut, and immediately averts his gaze after seeing the skin start to pull together again. He’d rather get stitches. The process might be a touch more painful, but it’s a lot less unsightly than medicinal magic in any degree. Some biological processes aren’t _meant_ to be seen so up-close.

 

“You’re such a baby,” Yaku snorts. “This is literally the same thing your body would be doing naturally anyway.”

 

 _“Naturally,_ it wouldn’t be going fast enough for me to see what’s going _on,”_ Tetsurou says. “This is disgusting. You’re seriously sick to want to see this all the time.”

 

“I _don’t_ want to see this, ever,” Yaku says. “In fact, having no patients — especially when they’re you — would be the ideal. No injuries to heal means no one’s getting hurt in the first place, which means everyone is very much happy, healthy, and alive. _You’re_ the sick one to subject me to this all the time.”

 

“You think I volunteered to have someone stick their makeshift knife in me?”

 

“With a personality like that, didn’t you?”

 

Tetsurou glares, but Yaku’s too satisfied with himself to even notice or care. He just carries on, sealing up his wound, and putting whatever spells over it to ensure Tetsurou’s health and safety or whatever. Maybe he’s cursing him. It wouldn’t come as much of a surprise.

 

Eventually, Yaku pulls his hands away, and hands Tetsurou his shirt. “Don’t go anywhere. I’ve still got to finish filling out your report, and find someone to make sure you get home safely.”

 

Tetsurou flashes a false smile and bats his eyes. “Oh, _Yaku,_ I just knew you secretly cared about me. I’m so touched. _So_ touched.”

 

“I’ll seal your mouth shut,” Yaku warns him. “Don’t even try it.”

 

“It’s just the two of us,” Tetsurou goes on, even if he can’t guarantee that the threat is an empty one. “It’s okay to let your true feelings out, I won’t tell anyone.” Yaku sticks his head out the door and calls for Kai, ignoring Tetsurou entirely. “I know you secretly love when I make my visits over here. Heart of gold, Yaku, you’ve got such a heart of gold.”

 

Kai comes in then, looks between Yaku’s scowl and Tetsurou’s grin, and sighs. “Whatever you gave him, you gave him too much.”

 

“My head is _spinning,”_ Tetsurou says, nodding. “Yakkun’s really got it in for me.”

 

“Just keep an eye on him,” Yaku says. “I’ll be back in five minutes. Don’t let him get up.”

 

The door closes behind him, and Kai settles his gaze on Tetsurou. “One day, he really is going to kill you, and you’re going to be the only one to blame.”

 

“Oh, c’mon,” Tetsurou says, waving his hand in dismissal. “Like he’s even got it in him. He’s too much of a coward to harm anyone. Little angel baby boy.”

 

Kai quirks an eyebrow. He looks like he might smile, but it would be highly unprofessional, so he doesn’t. “What _did_ he give you?”

 

Tetsurou shrugs. “Dunno, but it feels real good. Don’t let him send me off with any. I’ll end up stabbed again for a potion like this, and I think Yakkun is _quite_ sick of me. Don’t you think? I think so. Did you see his face?”

 

“Maybe he just hates seeing you here so often,” Kai says, carefully sitting down on the edge of Tetsurou’s cot. “The rest of us do. You’re terrible at keeping yourself safe.”

 

“I can either keep myself safe, or the rest of the city, you’ve gotta pick one,” Tetsurou says. “And I think all the other lives out there out-value mine, just based on, y’know, sheer number ’n’ all. One versus thousands. And don’t sit there and act like I asked for this, either! I didn’t tell him to stick a knife in me, you know. You know how much it hurts when Yaku does his thing? Because it hurts. Not even whatever the hell potion this is can mask _that.”_

 

“I think he does that on purpose,” Kai says.

 

Tetsurou huffs. “Little shit.”

 

True to his word, Yaku isn’t gone long. Within five minutes, he’s back with a packet of papers, a small pouch of pills, and a bottle of water, telling Tetsurou to get out of his office and not to show his face there again for at least another month.

 

“I make no promises,” Tetsurou tells him, leaning heavy against Kai’s side. “Crime never sleeps, you know. No rest for the wretched.”

 

“Wicked,” Kai corrects.

 

Tetsurou waves him off. He’s starting to feel drowsy. Yaku really did hit him with something strong. “Same difference. Be nicer to your other patients, or you’ll go out of business.”

 

 _“Goodbye,_ Kuroo,” Yaku says, waving his fingers, and Tetsurou feels himself nudged forward. “See you later, Kai. Get him home safe.”

 

“How thoughtful,” Tetsurou sniffs, wiping at a fake tear. “Get some sleep, Yakkun! Take care of your own health, too, eh? You look more like death every time I see you, it’ll drive away all your patients one day.”

 

Yaku rolls his eyes and shuts the door in his face. Which, rude.

 

“You ought to give him a break,” Kai says, helping him walk across the lot to his car. “He’s nicer than you deserve, helping you every time you try to get yourself killed.”

 

“I’m jus’ tryin’ to save the city. Not my fault no one wants to let me.”

 

Kai rolls his eyes and unceremoniously shoves Tetsurou into the front seat of his car, going so far as to buckle his seatbelt for him before closing the door and circling around to the driver’s side. “Just be careful,” he tells him once he’s settled in his own seat. “We’d hate to see anything serious happen to you.”

 

“Yeah, yeah. I’ll be careful.”

 

Kai gets him home and in his own bed, makes sure he knows when to take his antibiotics, and tells him Kenma will be by shortly to keep an eye on him before leaving. Tetsurou barely does more than sleep for the next two days, and when he checks later, there isn’t even a scar left behind where the knife had gone in.

 

* * *

 

Tetsurou is a good cop. He worked hard all through school, studying law as late into the night as he practiced enforcement magic. He’s closed more cases than almost anyone else in his precinct, not counting the detectives who’ve been there twice as long as he has, naturally, (but almost, when he really thinks about it), and he’s rarely _rarely_ let a criminal slip through his fingers. He’s a good cop and a diligent worker, and he’s proud enough to own up to that.

 

But all the files, all the _paperwork,_ the reports he has to file and read through — that’s all an entirely different story. If there’s any sort of spell to make the process go by faster, he has yet to discover it. It is, actually, entirely mind numbing. Moreso then Yaku’s strongest potion.

 

“You’re just being a baby,” Kenma says, not looking up from his DS. “It doesn’t even take an hour, Kuro. You just spend so much time whining that you drag it on forever.”

 

“Look at this,” Tetsurou says, waving the top paper in his face. “There are three sections on this form _alone_ that I have to fill in with the same report. What’s the point in that? What’s the point?”

 

“First of all, if it was all the same, then it shouldn’t take so long to fill out, since you don’t have to think of three whole answers to it, you already have the one.” Kenma carefully taps at the DS buttons. Tinny music comes out of the speakers. “Secondly, it’s not all the same, there are variations. This one doesn’t even ask about sustained injuries, and this one is, like, a single line summary. Again, you’re just being a baby.”

 

Tetsurou drags out a long sigh, leaning back in his desk chair. “How are you so out of things to do that you have time for Animal Crossing?” he groans. “That’s not fair.”

 

“I’m not out of things to do,” Kenma says. “I just can’t do my work, because I have to wait for you to finish these reports before we can go out investigating the burglary case. You’re inhibiting my ability to get anything done.”

 

Another sigh. He wants to be out investigating. Far more exciting. At least, it means leaving the precinct, and talking to other people, and maybe even Kenma letting him pick what music they listen to on the car radio as they head across town.

 

“You’re wasting time, you know. You could’ve had this done twenty minutes ago if you’d actually been working instead of having chair races with Tora.”

 

“That was productive!” Yamamoto chimes in from across the small office. “I won!”

 

Tetsurou spins around in his chair, slamming his feet onto the floor to keep from turning too far with the momentum. “You did _not,”_ he argues, jabbing a finger in Yamamoto’s direction. “You cheated.”

 

“I didn’t cheat, you just have no leg muscle.”

 

“You cheated.”

 

“He didn’t cheat, Kuro.”

 

“I didn’t cheat.”

 

Tetsurou narrows his eyes and flickers his gaze between the two of them. He settles finally on Kenma. “I liked you a whole lot more before you started dating him. You used to side with me, you know.”

 

“I side with whoever’s right,” Kenma says, even though that isn’t true. He sides with whoever’s going to buy him dinner. “Shut up, do your work, I wanna go before traffic gets too heavy.”

 

It doesn’t take that long, really, once Tetsurou actually focuses in on the paperwork. Contrary to what Kenma has to say about it, half the responses _are_ entirely identical, and a complete waste of energy to fill out. There are so many more interesting things to be doing with his time, even if all of this is equal in terms of importance. He can’t even use magic for any of it, which makes it that much more of a drag.

 

Out in the field is a different story. He’s practically buzzing when he drops his folder on Nekomata’s desk and turns to snatch his jacket off his desk chair, pulling Kenma along towards the door. Truth and deception spells, illusions, enhancements. This is Tetsurou’s favorite part of his job. His favorite part of _life._ Anything he can throw a little bit of magic into, he’s happy with.

 

Kenma tells him he’s wasting his energy with half of it, and Yaku agrees every time he shows up to his office not only injured, but entirely drained, but it’s fun. Tetsurou is having fun. They just don’t see the enchantment with it all.

 

(“I think it’s pretty fucking enchanting that you aren’t dead right now,” Yaku has tried to argue with him before, sealing up bullet holes and getting his blood flowing in the right places again.)

 

Kenma settles into the passenger seat of Tetsurou’s patrol car, pulling Tetsurou’s jacket over his lap, and their case file over that. He flips through the papers and photographs, skimming over it all while Tetsurou finds the radio station he wants.

 

An easy afternoon. It should be, anyway. Just investigating. Going through crime scenes, asking questions, maybe adding more clues to their file, zeroing in on specific suspects, eliminating others. That’s the ideal.

 

Over the course of the past couple of months, there have been a string of robberies at various clinics and specialty shops spanning the entire city. There was no discernible pattern at first, until Yaku made some offhand comment while setting Tetsurou’s broken arm about potions of healing, supply and demand, and how the demand had become greater than the supply, and sorry that he was going to have to take a couple days off and make another visit to his office.

 

Tetsurou had mentioned it to Kenma. Kenma had circled back through the burglary reports, and circled the common components.

 

They weren’t sure of the endgame quite yet, but someone was making healing potions increasingly more difficult to come by, and even more difficult to make. Crisis would set in sooner or later, if they couldn’t put a stop to it.

 

“I say we start with Suga-chan,” Tetsurou says, sparing a glance towards Kenma. “He’s most recent, and Sawamura was just upstairs when the break-in happened. There’s a chance he saw something he hasn’t realized.”

 

“That’s fine,” Kenma says. “I’ll get him to do some talking, you can poke around, or whatever.”

 

“You make it sound sinister,” Tetsurou snorts. “Play nice with Sawamura, yeah? He’s been through enough as it is.”

 

“You _put_ him through enough.”

 

Tetsurou bites back a grin. “That’s not my fault. I don’t know what gave him the idea I was there to arrest him, but it’s not my fault. You know that.”

 

Kenma gives him a look, and Tetsurou really does grin this time. He’s got no clue where Sawamura got the idea into his head, seriously, but he definitely did play it up. Sugawara was amused, at least.

 

(He’s grateful for that much. Had he not found it funny, he could have and likely would have done more harm to Tetsurou than even Yaku could ever dream of. Sugawara’s magic is strong, and he can be beyond terrible when he wants to. It’s almost admirable.)

 

It takes twenty minutes to get to Sugawara’s small shop, and he’s sitting right at the front counter when they step inside. They haven’t even told him the reason for their visit before he’s calling Sawamura to come down from their apartment above.

 

“They’re back to arrest you,” he murmurs into his phone. There’s a beat, and then he’s cackling with laughter, nearly tipping back out of his seat. He sets his phone down and leans forward on the counter, smiling up at Tetsurou and Kenma. “He’ll be right down. Not sure how happy he’ll be to see you, but he’s coming. Make any new breaks?”

 

Tetsurou shakes his head. “There haven’t been any new dots to connect. We’re hoping Sawamura can help with that, and we’ve got another couple visits to make after. Chances are, someone saw something. Or at least can give some sort of hint towards the purpose of it all.”

 

It’s not like there’s a surging need for medicinal potions at the moment. At least, no more than usual. There’s no market to make a fortune off of at this particular moment, so it’s puzzling, to say the least. Not to mention, no one’s necessarily _relying_ on potions for day-to-day needs. There are plenty of other alternatives.

 

There are footsteps on the stairs, and Tetsurou looks up. “Sawamura-kun! Miss me?”

 

“Like a toothache.” Sawamura returns his easy smile, though, so Tetsurou takes it lightly. “How can I help?”

 

“Can I ask some questions?” Kenma says. “I, um. Have a spell I’d like to try, if that’s okay.”

 

Sawamura nods, and leads Kenma into the back room to speak in private. Tetsurou turns back to Sugawara and leans onto the counter to mirror him.

 

“What’s Ken-chan wanna try, huh?” Sugawara asks. “Anything that’ll help more than the last time?”

 

“He’s got this memory spell,” Tetsurou says, waving a hand. “You know. Smartass always coming up with something new. Think Oikawa might’ve helped him.”

 

“It’s got to do with invading people’s minds,” Sugawara says. “Of course Tooru-chan’s involved.”

 

Tetsurou snorts and leans back, scanning the rest of the shop. It was broken into a week ago now, but it looks like Sugawara has patched up all the damages. There’s still stock clearly missing, waiting to be shipped in, but nothing looks particularly worse for wear anymore. No broken glass or shelves taken off the racks. Sugawara himself looks better, too. He’d been frantic when Tetsurou and Kenma had first arrived after his initial call, but he’s back to his same, serene self now.

 

It’s relieving. Seeing Sugawara in a panic is more unsettling than anything else. He’s always the one with his head high and spirits lifted. If he’s off, then there’s a much bigger problem at hand.

 

“I was talking to Yakkun earlier,” he says after a moment. Tetsurou frowns. He already knows Sugawara’s going to depart him with some sage advice, or brilliant little bit of wisdom from Yaku, because of course he’s got all the answers. “I think you should stop by to see him sometime. He was doing some reading, and came up with a theory I think you’ll want to hear. Even if it’s wrong, it might still be helpful.”

 

“Yeah, yeah.”

 

Sugawara narrows his eyes. “I mean it. I’m gonna tell Kenma, too, so I can make sure you go.”

 

“I’ll go!” Tetsurou says. “I’m not going to be happy about it, but I’ll go.” It’s for the better of the people, he has to remind himself. He doesn’t have to like it, or be particularly thrilled about it, but if there’s a chance it’ll help solve this case and keep other people safe, he’ll do it. This is, after all, exactly what he signed up for. Like it or not, he isn’t left with much of a choice.

 

Sugawara flashes a grin. “Good. Let me know what you think of it, okay? I’ll sleep easier having your professional opinion.”

 

For that — for Sugawara to sleep easy — he’ll do whatever it takes.

 

* * *

 

“You can’t be serious.”

 

Kenma only shrugs. “It’s date night. Sorry you have no love life to speak of, other than being married to your work.”

 

“That hurts, Kenma.”

 

“Truth does that. I’m sure Yaku-san will want you out quick, too. He’s not going to drag this on and make this even more painful for the both of you.” Kenma leans down into Tetsurou’s window, leaning onto folded arms. “You said it yourself. Even if you don’t see the big picture yet, it’s likely going to be bad. You want to prevent it, yeah? So talk to Yaku-san. Play nice. You can come by later, if you want.”

 

“No, it’s fine,” Tetsurou sighs. “I won’t interrupt your date night.”

 

Kenma’s eyes light up. “Good, because I wasn’t serious. No offense, but I really only wanted to spend time with Tora tonight.”

 

Tetsurou rolls his eyes. “Now I really will come by. Brat.”

 

To that, Kenma smiles, and steps back from Tetsurou’s car. “Drive safe, okay? I’ll see you Monday.”

 

“Yeah, see you Monday. Enjoy your date.”

 

“I will, without you, thanks.” Kenma leaves looking particularly pleased with himself, and Tetsurou sinks further into his seat.

 

He was kind of counting on Kenma to play mediator going to see Yaku. But technically speaking, the day is over, and Kenma has plans, while Tetsurou does not, and as terrible as it is, going to talk to Yaku is marginally more exciting than spending the night alone at his apartment, battling his cat for the remote.

 

Yaku’s still at his office, of course. Tetsurou’s not sure he ever actually leaves. He acts like he’s bound to the place. He’s always there when Tetsurou needs him. Two in the morning or two in the afternoon, he’s always ready to mend him.

 

He wonders if he really _is_ bound to the place, sometimes.

 

He doesn’t look surprised to see Tetsurou. He never does. He might be surprised there’s nothing bleeding or broken, though, if Sugawara hasn’t told him Tetsurou planned to come by.

 

“What do you need?” Yaku asks.

 

“Why do you assume I need something?” Tetsurou replies. “How do you know this isn’t just a friendly visit?” Yaku gives him an unamused look. Tetsurou drops down into the chair on the other side of Yaku’s desk. “Wonderful point. Nothing broken, if you were wondering. I’m not showing up dying at your doorstep.”

 

“Too bad.”

 

“You’re so sweet, Yakkun,” Tetsurou coos, voice lilting. He reaches over to pinch at Yaku’s cheeks, even if his hands are swatted away before he makes it. “So cute, so kind, so caring. I truly see why you’re the city’s highest rated.” He settles back into his chair, shifts. It’s a little uncomfortable, actually, coming to just _talk._ He’d rather have something for Yaku to mend. “Suga-chan said you had some thoughts on our robbery case.”

 

“Mm. I do. I was hoping you’d have Kenma-kun with you for this. The real brains, to make sense of this.”

 

_“Hey.”_

 

Yaku looks far too pleased with himself. “I— Yeah. I was reading through some medical journals, and happened to come across something interesting, so I did a little digging. I don’t know how much any of it actually means, but I thought it could maybe help.” He pulls a folder from the edge of the desk, thicker than anything Tetsurou would have expected, considering his research was supposedly not even intentional. He hands it to Tetsurou, and waits a moment for him to scan through some of the pages before elaborating on any of it. “Do you remember, that freak outbreak in the states, around two years ago? And the one in France a couple before that?”

 

Tetsurou gives a slow nod as he flips through the packets. Isolated incidents. Bursts of illness, unnamed diseases, and a race to find any cure. Both cases had happy endings — only a total of three deaths between them. Which, while still tragic, could have been much worse than it was.

 

“There’s more to it,” Yaku says. “Korea, before France, and Italy before Korea. A little more serious, and a little harder to cure each time. Never the same exact disease, but similar strands. I think someone’s trying to cause an outbreak, and trying to prevent anyone from being able to cure it. There’s a ton of reports in there, and some dating back even earlier, but I don’t know how related those are. I don’t know. Maybe it’s got nothing to do with it, but I figured, if it did, you should know.”

 

Tetsurou takes another few minutes to read through. There’s more than just medical journals; he’s included all the related police reports and news stories. He had to have done serious research. All this, based purely on a whim.

 

“You looked into all of this?” He finally lifts his gaze to Yaku, sitting patiently on the other side of the desk.

 

He shrugs. “I thought it might help. I don’t want to see anything breaking out here. Whatever strain this is bound to be will only be worse than the last one. The more you have to catch whoever’s behind it, the faster this can get closed. I did contact some of the other doctors involved, to try and recreate some of their potions, and remedy them into one of my own. Taking precautions, I guess.”

 

Tetsurou might not particularly _like_ Yaku. There’s a lot they don’t agree on, and he’s got an attitude about him that Tetsurou doesn’t appreciate, and he lectures him far too much every time he shows up to his office. But he has to admit, he’s good at what he does, and he’s committed. It’s admirable.

 

“Give me a couple days to read through all this,” Tetsurou says after a moment, “and I’ll call you. I think you might actually be right about this.”

 

* * *

 

Despite his intentions, the next time Tetsurou sees Yaku is not on his own terms, nor is it related to their case. Rather, the next time he’s at Yaku’s office, he’s wrapped haphazardly in too much gauze, his whole left side burned, and a bone-deep ache settling in.

 

“Care to explain?” Yaku says, wheeling his chair over to the cot Tetsurou can’t even lay flat onto.

 

“I caught him.”

 

Yaku snorts, rolling his eyes. He lifts the gauze from his arm, inspecting the damage. His whole demeanor changes when he’s working. He’s more serious than what suits him, Tetsurou thinks. He remembers that he’s not the only person Yaku takes care of, and wonders how much worse he has to deal with on a day to day basis. He’s highly regarded, and only really deals with the most serious cases, Tetsurou knows. Worse than his own issues, that he would take elsewhere if it weren’t for Yaku’s close relation to the police precinct.

 

Too much stress will break him. Tetsurou might be a little concerned.

 

“Of course you did,” Yaku says, peeling back more of the bandages. “And what did he have on you?”

 

Tetsurou’s breath hitches when Yaku’s fingers ghost across damaged skin, getting a feel for the injury. He lifts his gaze to the ceiling, unable to watch Yaku work. “He, y’know, was really good with— _ah,_ be gentle—fire magic. He lit the whole place up. Oikawa’s team showed up in time to minimize the— _Jesus,_ Yakkun—“

 

“I’m being as careful as I can.”

 

“I _know,_ just—“ Tetsurou sucks in a breath. “They minimized the—the damage, and Yamamoto and I caught him.”

 

“And where is he?”

 

“Worried about him?” He wishes more than anything that Kenma were there, to give him a hand to hold. Or to just _be_ there. Kenma’s always given off a comforting aura, and always makes these visits to Yaku’s more bearable. Kai might be out in the waiting room, but he’ll never come back with Tetsurou. He’s even more squeamish than he is. “He’s fine. He didn’t get caught in it. Kenma took him to visit a general clinic, and he’s home already.”

 

Yaku hums, and turns to take a bottle off the counter. “You can drink this, but it’ll still hurt. He got you bad.”

 

“Yeah, yeah, I know the drill. Try to make it quick.”

 

“Can’t be quick and also be careful,” Yaku tells him. There’s a beat. “I’ll try to make it easy on you.”

 

Tetsurou can’t tell whether he actually does or not. It still hurts, and he still refuses to look at the process after daring a brief glance at the blisters popping on his shoulder. He doesn’t know how Yaku stomachs any of this. All the cases he deals with on a daily basis, and Tetsurou doesn’t understand how he bears it.

 

He gives Tetsurou another potion to drink after he’s through, and instructs him not to move before he leaves the room. Tetsurou looks to find his skin perfectly clear, if still a touch red and tender. No marks. Yaku never leaves any marks. He’s clean and efficient and careful, and Tetsurou knows he’d be a lot worse off without him.

 

He downs the potion, chases it with the water on the table beside him, and tugs the blanket on his lap up to his chin. He could sleep for a few days, probably, with how drained he feels. Everyone else would probably let him. But there are more cases. There’s still work to do.

 

He still has to talk to Yaku.

 

There are eighteen unread texts on his phone, ten of them from Kenma. Checking on him, as if he doesn’t already know he’s being taken care of. As much as Kenma refuses to act like it, he’s always worrying. Always caring. Soft, despite his typical actions.

 

He sends him a quick update, and texts Kai to ask if he’s still waiting there (he is), and eventually circles back to his notes app, reading through everything he wrote down over Yaku’s research. He’d barely slept the next couple nights after meeting with him, poring over all the journals and reports. It was terrifying to think something so monstrous was knocking on Tokyo’s doorstep. Worse to think about what might happen if they couldn’t stop it before it hit.

 

Three is already too high a death toll.

 

Yaku comes back in a few minutes later, holding his clipboard with all Tetsurou’s medical information. He sits back down beside him and jots down the last remaining notes for today’s visit.

 

“You know,” he says after a moment, “I’d appreciate it a lot more if you stopped coming in here like this. One day you’re going to come in here with something I can’t fix.”

 

“You _do_ care,” Tetsurou says, eyes wide and teasing. “I’m so touched.” Yaku swats at his arm, and he winces, but grins despite himself. “And I thought you were supposed to be Japan’s best. You’re telling me even the great Yakkun can be defeated by little old me?”

 

“Careful, or I might take that as a compliment,” Yaku says. “Don’t start being all nice just because you’re drugged up.”

 

“I’m always nice.”

 

Yaku shoots him a pointed look, as if to say _yeah, right_ before returning his attention to his clipboard. “Whatever helps you sleep at night.”

 

Tetsurou tries to look snarky, but whatever Yaku gave him is really starting to kick in, and he’s feeling too loose to know if he manages anything close to what he wants. “Hey. Hey.” He waits for Yaku to give him his full attention. “I read up on everything you gave me. I think you’re right. I mean . . .” His vision is starting to go a little hazy at the edges. “I mean there’s still a chance that it’s something else. But with all the similarities, and the time frame, I think you might’ve found a real lead.”

 

“Yeah?”

 

Tetsurou wrinkles his nose. “Don’t look too pleased with yourself. You got lucky.”

 

“Very lucky, thank you.” Yaku sits a little straighter in his seat. “So you’re going to follow this thread? I can give you the contact information for some of the other officers and researchers from the past cases. And I can give you my notes on what I’m working on.”

 

“That— Yeah. That would be . . . What did you _give_ me?”

 

Yaku huffs a little laugh and stands up, making the decision to continue this conversation later. “Sleep, Kuroo. Your body’s tired. I don’t know how much magic you used through your chase and arrest today, but you’re completely drained. So sleep, and we can talk in the morning.”

 

He thinks he gives a tired smile. “I knew you cared about me, Yakkun.”

 

* * *

 

He spends approximately as much time working with Yaku on the case as he does Kenma. Days are spent following leads, conducting interviews, searching crime scenes, and conducting research. And nights, after Kenma’s gone home, when Tetsurou has nothing to return to, he finds himself in Yaku’s office.

 

They don’t stay long, at the start. A couple hours at most, to research, and Yaku makes notes on different potions he’d like to try mixing, and then they part ways and go home. But the weeks go on, and the hours draw later and later. They don’t always stay cooped up in his office, either. Sometimes they walk down the street to a café. Sometimes Yaku meets him in the precinct before Tetsurou’s day is over, and they’ll stay there for hours instead, refilling cups of cheap coffee and battling over the last stale donut.

 

It’s not bad. Yaku’s a smartass about everything, and never wants to just _split_ the last donut as if to share would be such a curse, but there are some evenings that are just quiet and easy and nice, and Tetsurou feels like they might actually be getting somewhere.

 

“It’s so cute to see you two actually getting along,” Kenma comments one morning as they’re walking to the train.

 

“You saw the bruise on my arm, didn’t you? You are aware that he did that?” Kuroo rolls up the sleeve to his t-shirt just to prove his point. “Over _croissants_ of all things. And you want to call that cute.” He lets his sleeve fall back over his arm, hiding the fist-sized bruise from sight again. “He didn’t even have the decency to heal it for me.”

 

“Waste of magic,” Kenma says. “And I can’t particularly blame him when you were the one trying to steal his food.”

 

“Unbelievable.” Tetsurou throws his hands up in disbelief and starts taking longer strides forward, leaving Kenma lagging a half-step behind. “You really are turning on me. Taking Yamamoto’s side was one thing, but Yaku? _Kenma.”_ He turns on him, shooting him a disappointed look. “After all we’ve been through, really. I would never turn on you like this, you know.”

 

“Last week you sold me out for cheating against Tooru in cards,” Kenma says flatly. He carries on walking past Tetsurou. “And the week before that, you teamed up against me with Tora to force me to eat peppers.”

 

“You weren’t supposed to find counterpoints,” Tetsurou pouts.

 

“Not my fault you’re stupid.” Kenma swipes his transit card to get into the train station, and Tetsurou follows. “Are you meeting with Yaku-san tonight? I have some notes about healing potions to give him. I’m sure it’s nothing he doesn’t already know, but in case it helps . . .” He shrugs. “Nothing’s really useless, I guess.”

 

“Yeah, I’ll pass them along,” Tetsurou says. Kenma finds a seat on the next train, and Tetsurou stays standing in front of him, hand loosely gripping the overhead bar. “I keep feeling like some of these nights are more or less useless. We haven’t made much headway in a week. At this point it’s just like pulling teeth, sitting around reading the same reports, and listening to him make his smartass comments.”

 

Kenma hums. “Tiger’s cave. Greater suffering, greater reward.”

 

Tetsurou rolls his eyes. Kenma spouts all his little bits of wisdom and lame idioms, and even if they might be true, they don’t help to ease Tetsurou’s pain any.

 

“Look, just— You’re making a lot of progress. You’re talking to that scientist in France, aren’t you? They’re supposed to get you those other reports sometime this week, and that’ll help push you forward. At the very least, Yaku-san can look into his potion recipe a little more. Did you hear from that US officer yet?”

 

Tetsurou nods. “He sent an email this morning, I’ll read it when we get back. I’d rather focus on this case for now. I could use a little breathing room from that for now.”

 

So Kenma drops it, and pulls up a game on his phone to occupy the train ride. Still, he makes his snarky comments when Tetsurou gets a cryptic text from Yaku halfway to their crime scene.

 

It’s not cute. They’re _barely_ getting along.

 

Still, Tetsurou will admit, he doesn’t mind Yaku’s company quite so much at this point. It’s not anywhere near enjoyable, but it’s more than just simply bearable. It’s _alright._

 

They meet at Yaku’s office, long after the sun has gone down. Yaku doesn’t ask, but Tetsurou offers up that he’s so late because an interrogation ran far longer than he thought it would, and then there was booking, and reports, and when it comes down to it, it’s far more information than he has to give Yaku at all, especially when he doesn’t even seem to care about how late Tetsurou’s shown up. But it would bother Tetsurou too much to let him think he just didn’t care, or value Yaku’s time.

 

There’s something to that particular thread of feeling, but he doesn’t let himself dwell on it.

 

The French scientist got back to Yaku, finally. “I want to make some adjustments to his potion, based on the US doctor’s notes, and what Kenma’s given me,” he says. “You don’t have to, obviously, but would you be, like, opposed to trying it? It probably won’t do much for you, since you’re not dying, as far as I’m aware, but I want to test for possible side effects.”

 

“So I’m your lab rat now?” Tetsurou says. “I see.”

 

Yaku rolls his eyes. “I said you didn’t have to. I can always do it myself, or ask, I don’t know, Inuoka.”

 

“No, shut up, I’ll do it.”

 

Yaku throws up his hands in exasperation and turns away, going back to the materials on his desk. “I can’t stand you,” he huffs.

 

“Hence why you’re sitting.”

 

Tetsurou knows it’s a terrible joke the second it leaves his mouth. It wouldn’t even make Lev laugh. But he sees Yaku’s shoulders jolt, and hears what sounds like a snort, and finds himself biting back a grin.

 

“Did you seriously laugh at that?”

 

“What? No. Why would I— Shut up, you’re so lame.”

 

Tetsurou’s lips curl upwards, and he dangles himself over Yaku’s shoulders. “Oh, _Yakkun._ I’m so touched. _So_ touched, that you think my lame jokes are funny. You must really like me. That’s so cute.”

 

Yaku glares and covers Tetsurou’s face with a hand, shoving him back. All Tetsurou can do is laugh.

 

“You’re such a pest. Maybe I will call Inuoka.”

 

Tetsurou feels something jolt in his chest. “Excuse you! You don’t get to replace me that easy. I’m your lab rat, just me.”

 

There’s a sharp, singular _Ha!_ from Yaku, and he glances over his shoulder. “Right, okay. Then shut up and let me work, or I won’t be trying anything on you tonight.”

 

Tetsurou’s beyond tempted to keep disturbing him, but it would only really mean impeding progress on his own case, which is entirely pointless. So he sits back in his own chair and lets Yaku work, flipping through some of the papers on his desk to occupy himself. Maybe there’s something he’s missed the last eighty times he read these reports.

 

It only takes so long before Tetsurou gets bored, and he rolls over to Yaku’s side, peering over his shoulder at the variety of bottles he has spread in front of him.

 

“You’re mixing pine into this?” Tetsurou asks, quirking an eyebrow. He can’t remember that ever appearing in any healing potions he learned.

 

Yaku spares him a glance out of the corner of his eye. “I’m going off the new reports. What do you know about potions anyway, huh? Mr. Detective.”

 

Tetsurou scrunches his nose. He hates when Yaku calls him that. Like he doesn’t know anything about the finer tuned points of magic, the math and chemistry side to it, purely because he spends most of his days working with spoken spells and the occasional summoning circle.

 

“I know quite a lot, actually,” he fires back. “I was originally studying medicinal magic, thank you very much. Potions happened to be one of my specialties.”

 

This gets a little more of Yaku’s attention. Tetsurou sits up a little straighter, pleased with himself.

 

“Oh?” Yaku’s still got his gaze focused intently on the potion he’s mixing, but it’s clear he’s listening with full attention.

 

“I’m good at chemistry,” Tetsurou tells him. “I’ve got the periodic tables memorized, you know. Both natural and supernatural. I was midway through developing a potion for matter shifting when I changed my course of study, and had to transfer out of the class.”

 

Yaku finally turns to fully face him. “Matter shifting? How would that work?”

 

Tetsurou is _beyond_ pleased with himself at this point. There’s something about having Yaku’s full, undivided attention that’s getting to him. “To take, like, a gaseous form. It’s more or less just to, like—“ He pauses, trying to find the proper way to explain this. Trying to word his ideas has never been his strongsuit. “I guess, like, invisibility lets you slip through light, right? None reflects off you. Same concept, but with solid matter. It’d let you slip through solid forms, like a vapor, for a time.”

 

“Why’d you switch out in the middle of that?” Yaku asks. His voice is somewhere a little farther away, lost in thought.

 

“Mm . . . It’s kind of a layered story,” he tells him, choosing his words carefully. He thinks of his mother’s eternal absence, and of his father. He thinks of a call that came in at three in the morning with _answers,_ after more than a decade, and how knowing seemed to ache more than living with the mystery of what happened.

 

“Layered,” Yaku echoes.

 

Tetsurou nods. “It’s not like it’s particularly long or complicated, there’s just a lot to it, I guess. More or less, I decided I wanted to take more action, in a way that I was never going to get to working for a medical clinic, or whatever. Just a bonus that law enforcement gets to summon their familiars to work cases.”

 

Yaku snorts. “Yeah? And how come I’ve never seen your familiar before? How come it’s not protecting you from trying to burn yourself to a crisp for some stolen jewels?”

 

“Okay, first of all,” Tetsurou says, leaning forward with a pointed finger in Yaku’s face, “those jewels belonged to the Japanese ambassador’s daughter, who is a very large benefactor to cat shelters all over the country, not to mention a very talented witch who needed them for, like, a potential cure to global warming.”

 

“Glad you listed those details in order of importance.”

 

“Don’t interrupt me.” Yaku’s lips quirk into half a smile. “Secondly, my familiar is . . . not ideal for such situations.” Tetsurou averts his gaze, feeling his face heating.

 

“Please, go on.”

 

“I think I’m good, actually, thanks.”

 

“No, no, I want to hear about this.” Yaku’s voice is lilted with laughter now. “Tell me about your familiar, Kuroo, what form is it?”

 

Tetsurou mumbles so low that Yaku will definitely miss what he says, confirmed when he asks him to repeat himself.

 

“It’s a shyx,” Tetsurou says, barely any louder or clearer, but Yaku catches it. His whole face lights up.

 

“Oh my god.”

 

“Don’t.”

 

“Oh, my god.”

 

“Yakkun. Please.”

 

“No, no, nothing!” Yaku waves is hands in front of him, trying to clear the air, even as he lets out a helpless little laugh. “Just cute, is all, that you have a tiny little _cat_ as your familiar.”

 

“Shyx are more like fennec foxes than cats, if anything,” Tetsurou tries to argue, even though there’s nothing that will really help his case at this point. It’s not even like he’s embarrassed about it or anything. Maybe the first time he summoned it, back in university, but he’s long since realized having a shyx for a familiar is kind of kickass. They’re feisty as hell, and one of the most nimble creatures to exist. He loves his.

 

It’s just that he knows it by no means reflects what everyone always thinks is familiar would be.

 

“That’s so sweet. Can I meet it sometime? ’s it got a name?”

 

This, if anything, is the only embarrassing part about it. “Shinx,” Tetsurou sniffs, shifting his gaze off to the side.

 

Yaku blinks. “Like . . . like the pokemon.”

 

Tetsurou nods. “Like the pokemon.”

 

Yaku purses his lips, nodding slow, and turns back to his potions. “The pokemon.” He shuffles a couple vials, pours one into his flask, and as he sets it back down, completely loses his composure, bursting out into a slew of giggles.

 

“It’s not that funny!” Tetsurou tries to argue.

 

“No, I’m sorry!” Yaku says, hands over his stomach. “Just— You’re so _lame!”_

 

“Excuse me!”

 

“Kuroo Tetsurou, detective extraordinaire, has a shyx familiar named _Shinx._ I can’t believe this.” Yaku fans at his face, trying to calm himself down. “I used to think you were some tough, pretentious asshole, but you’re really so _lame._ You memorized the periodic tables!”

 

“It’s useful! And a good party trick!”

 

“Party trick!” This sets Yaku off into another helpless wail of laughter, falling back against his chair.

 

Tetsurou isn’t even upset that Yaku’s laughing at him. It’s more amusing than anything else to see him worked up in such a manner, and a smile fights its way onto his own lips. Soon enough, he’s laughing right alongside him.

 

“You’re such an asshole,” Tetsurou says, no heat behind the words.

 

“And you’re such a nerd,” Yaku replies. “Oh my god.”

 

“Whatever! You’re just as lame. You spend all your free time with _me.”_

 

“You’re right, that’s so sad.” Yaku gives a mocking, self-pitying shake of his head, but he’s grinning despite himself. He pauses for a moment to gather himself, then glances between the potion-in-progress and Tetsurou. “Can we get dinner? I haven’t actually eaten, and this is going to take a while longer.”

 

Tetsurou shrugs. “Fine by me. I haven’t had a chance for it yet, either. I came straight here after I was finished with my work for the day.”

 

Yaku nods and pulls the jacket off the back of his chair. “Where to? I’m alright with whatever, really.”

 

Tetsurou follows him out the door, falling into step beside him. Whatever lingering tension there might have been is entirely dissolved now. He can’t convince himself that he actually dislikes spending time with Yaku like this, at this point. He’d almost go so far as to call it pleasant.

 

They settle on hot pot, since it’s close and convenient and overall _good._ Yaku asks more about Tetsurou’s sudden major shift, seeming genuinely interested, and Yaku tells him about all the work that’s gone into opening his own medical practice. They probably overstay their welcome at the restaurant, lost in the middle of their conversation, but make their way out before it gets too late.

 

Tetsurou’s midway through defending his so-called _needless_ use of magic while out in the line of duty. “It’s _cool,_ alright? How do you resist using magic when it’s just available like that?”

 

“You just love magic, huh?” Yaku smiles to himself. “Fucking nerd.”

 

Tetsurou snorts. “We’ve established that already, haven’t we? And how do you not? I used to, y’know, when Kenma ’n’ I were kids, pull off little tricks and things for him all the time. To cheer him up. He was sick a lot back then. I think that’s how I got set onto the idea of medicinal magic, since I didn’t know if this was going to be his whole life — just, sick all the time. He’s a lot better now, by the way. But, when he was sick, I’d do lots of little tricks for him, just to entertain him. Sparks from my fingertips, and little dancing lights, making things move on their own — things like that.”

 

“I wanna see this,” Yaku says. He stops in the middle of the sidewalk, turning to fully face Tetsurou. “I want to see your little magic show. _Dazzle_ me.”

 

“Are you serious?”

 

“C’mon, Mr. Entertainer, show me the lights.”

 

Yaku’s eyes are lit up. Tetsurou thinks about the world of stress he’s always imagined as bearing down on his shoulders, and the endless hours he spends in his office. How often does he get out for himself, Tetsurou wonders. Does he ever spend time with people like this, purposeless, away from his work?

 

He spends his life bettering the lives of those around him, healing their wounds, mending their souls. Who’s been there to make sure that in giving them new life, he’s not taking giving up his own?

 

Tetsurou pulls Yaku off to the side, so they’re not blocking the whole path, even though the streets are empty at this hour. He holds his hands palm-up between them, and lets balls of light bounce off the surface. They cast a pale glow across Yaku’s features, and put a bright twinkle in his eyes. He looks purely enchanted by such a trivial act of magic.

 

But then, this is the type of thing that made Tetsurou fall in love with magic, isn’t it? That he saw supernatural acts all around him, all the time, never fazed him much. It’s always been the petty tricks — the dancing lights, being able to make dishes put themselves back into cabinets — that made magic feel _real._ Like the mystical, fairytale sort of thing.

 

“Cool, right?” Tetsurou says, voice soft. He doesn’t want to break the silence, and shatter the mood.

 

He thinks, for a moment, Yaku’s going to denounce it for the easy, meaningless act it really is, but what he gets instead is a slow, mystified nod.

 

“Cool.”

 

* * *

 

They don’t always meet to work on their case. Sometimes, Yaku meets him at the train, and they’ll go to have dinner, and dance lights off the freezing lake. Sometimes, Yaku comes back to Tetsurou’s apartment with him, and they’ll work for an hour at most before Yaku settles back to play with his cat, and they’ll put on a documentary. He meets Shinx, and Shinx warms up to him in an instant.

 

There’s something here.

 

* * *

 

Tetsurou calls it something akin to friendship.

 

Kai calls it sweet.

 

Kenma calls it the tiger’s cub.

 

* * *

 

“All this talk about Yaku Morisuke being the most brilliant healer alive, a true prodigy, a master in his field, and yet, here you are, having tried to mix sulfur with _giratan blood.”_ Tetsurou leans in the doorway, eyeing the scene before him with no small amount of amusement.

 

“Do you ever shut up?” Yaku bites back, cradling his hand to his chest. His t-shirt is scorched.

 

“This is potion making 101 shit,” Tetsurou continues, ignoring him entirely. “Even Kenma knows those cause an adverse reaction, and he failed that class.”

 

“Why did I call you?” Yaku sighs, mostly to himself, eyes turned to the ceiling as if there’s some higher being present to give him the answer he’s seeking. “This is so stupid.”

 

“You are! Right!” Tetsurou grins at Yaku’s smile, and only takes another moment to enjoy this particular predicament before giving in and making a move to help him. He grabs a cloth off Yaku’s desk and wraps it carefully around Yaku’s injured hand, making sure it’s tight. Pressure is important. “Care to share how you ended up here?”

 

Yaku scowls, but the expression dissolves just as quickly as it appeared. He just looks . . . _tired._ “I haven’t slept in, like, three days. I’m physically and mentally and _magically_ exhausted.”

 

Tetsurou frowns. Thinks of the pressure he’s got to be under. His amusement has almost entirely disappeared. “You need to sleep, Yakkun.”

 

“I know.”

 

“I’m going to take you to get some sleep.”

 

“Okay.”

 

Tetsurou pulls Yaku off the floor and guides him to the couch at the edge of the room, and leaves him for just a moment to search through his shelves for a potion of healing. While Yaku drinks it down, Tetsurou cleans up the shattered glass and wipes up the spill on the floor, and tries to pull the papers on his desk into some sort of order. Yaku will probably have to fix it later, but for now, this will do. At least it’s less chaotic than how it started.

 

He helps Yaku get his uninjured arm into the sleeve of his jacket, and carefully settles the other end of it onto his other shoulder. He can’t find a sling, so Yaku will have to deal with holding his own hand for the duration of the car ride.

 

It’s just about entirely silent between the two of them, which leaves Tetsurou’s mind free to ponder the thought that, of all people, Yaku called _him_ in the middle of the night for help when he was in need. He asked Tetsurou to come to his aid, out of everyone in his life, and there is so much more weight to that than he knows what to do with.

 

“My apartment’s the other way,” Yaku says in a small voice as Tetsurou makes the turn out of the office’s parking lot. It doesn’t even sound like he cares so much. It’s more an observational note than anything.

 

“I never said I was taking you there,” Tetsurou replies. And that’s the end of that matter.

 

Tetsurou parks behind his own apartment building, and helps Yaku out of the car and up the stairs to his apartment. He seats him at the kitchen table, and goes off to find the first-aid kit in his bathroom. It’s not much, and probably not quite enough to properly treat Yaku’s wound, but it’s not like it has to be sufficient anyway. It just has to hold up until Yaku gets enough rest to regain the energy to fix himself with his magic.

 

Yaku holds his hand steady in Tetsurou’s as Tetsurou cleans and disinfects the cuts and burns spanning from his wrist to the ends of his fingers. There’s a few small scrapes up his arm nearing his elbow, but those have already scabbed over, insignificant.

 

“What were you trying to do?” Tetsurou asks as he works.

 

“I . . . I don’t know. I was trying to make adjustments to the potion.” Yaku’s gaze is fixed on their mixed hands. Tetsurou isn’t sure if he’s watching what he’s doing, waiting to correct any mistakes, or if he’s just . . . _watching._ “There isn’t quite enough in all the notes about the specific magic entwined with the virus, but I have a theory on how to fight against what _might_ be coming our way. But I wasn’t really considering all the different elements, I guess.”

 

“You guess,” Tetsurou repeats, but there isn’t any malice to it. He can’t bring himself to be anything but gentle at the present moment, when Yaku is like this. “You need to be more careful. You need to rest more. What were you trying to accomplish, driving yourself into the dirt like this?”

 

Yaku’s already small as he is, but he seems to shrink even further in this moment. “I don’t know.” There’s a pause, but Tetsurou knows he has more to say, so he doesn’t interject with anything. “I’m just scared. I don’t want this to hit us and be entirely helpless. I don’t want anyone to lose their life over this.”

 

“They won’t,” Tetsurou assures him. It’s the first real piece of vulnerability he’s seen from Yaku, and it twists something in his chest. “You’ve been working hard, and Kenma and I have been working hard, and no matter what, we’ll seal this before anything happens. We’ll catch whoever’s been trying to spread whatever plague before they can hit us, and you’ll create your perfect cure in the event that anything slips through the cracks. It’s going to be okay.”

 

Yaku nods. He’s still watching, biting down on his lower lip.

 

Tetsurou carefully wraps his hand in gauze, properly tying off the bandage. It will suffice for now. At the very least, Yaku’s not going to end up infected or ill.

 

“You need to sleep, now, Yakkun,” Tetsurou says. Yaku finally lifts his gaze to meet his eyes, and Tetsurou doesn’t trie to lie to himself — his breath catches, just a little, right on its way up his throat.

 

 _Ah._ The tiger’s cub.

 

Yaku nods, and lets Tetsurou lead him into his bedroom. He hands him one of his own old t-shirts, and a pair of Kenma’s left behind sweatpants, which are a little more likely to fit him than anything of Tetsurou’s. Yaku manages to change on his own, even if it takes a little longer than it normally might, and he only puts up a little bit of a fight when Tetsurou insists he takes his bed.

 

“I have a spare futon to roll out, it’s fine. You need the sleep more than I do right now,” Tetsurou assures him.

 

Yaku’s gone when he wakes up, but there’s a rambling thank you note on the kitchen table, and an IOU for lunch.

 

(He looks brighter the next time Tetsurou sees him. Perfectly healed, and awake, and cheerful. Yaku smiles at him over their shared meal, and Tetsurou thinks the sun would be less blinding.)

 

(“I can’t believe you have _feelings_ for Yaku-san,” Kenma scoffs, later. “Disgusting.”

 

“What, Yakkun?” Tetsurou says, a little offended on his behalf. He can’t even bring himself to argue against the accusation.

 

Kenma’s face twists up. “What? No. Feelings.”

 

“You’re literally in love with Yamamoto.”

 

“And what of it?”)

 

* * *

 

The next time Yaku calls him in the middle of the night, it’s to tell him he’s been called into the local hospital to look into a mysterious case. None of the other medical staff on call have been able to identify the disease the patient is suffering, and they don’t want to chance mistreating it and making anything worse. He tells Tetsurou he’ll keep him updated, but he has a gut feeling that something is starting. The next piece is in play, and they have to _move._

 

Tetsurou drives over to Kenma’s apartment first thing in the morning, ignoring protests of it being his day off, dragging Yamamoto out with him, since more hands on deck is more an advantage than anything. He calls Kai and Nekomata as well on the drive to the precinct, and by the time they show up, all heads are present.

 

He sends a slew of unanswered texts to Yaku, waiting for any new information. If this is really kicking off, he needs to know. He needs to formulate some sort of plan.

 

Nobody wants things to get worse than they already are.

 

“Fill us all in, Kuroo-san,” Yamamoto says, wheeling his chair over to Tetsurou’s desk. He looks over the mess of files and notes spread across the surface, trying to make sense of any of it.

 

Tetsurou scans over all their faces, and tells them everything. All the unnamed diseases, different on a surface level, but all sharing common components. An evolution of a base virus. Spread across the globe over the span of several years, to try and bury the evidence of the attempts. The strain of not having enough medical supplies to put together even a simple healing potion, much less something as complex as would have been needed, on top of the panic of the virus becoming widespread. How the seriousness of the issue increased with each attempt, and his and Yaku’s theory that, were it to hit here, it could have potential to spread.

 

And Yaku’s not positive they’ll be able to put a stop to it in time.

 

The next call comes in to say that four more patients have shown up, all exhibiting the same symptoms.

 

“We’ll split up,” Nekomata says, making an executive decision before Tetsurou’s even begun to formulate a plan. “You and Kozume have narrowed it down to a few potential suspects, and now is the time to settle it to one. Yamamoto and Lev can head to the west end, and check out the old medical center. You and Kozume can take your warehouse. Forget warrants. I don’t want to see any sort of death toll on this. You and Morisuke have worked too much on this for that.”

 

Tetsurou swallows and grabs his badge from his desk, snatches up his jacket, and leads Kenma out to his car, not sticking around to hear Nekomata hand out any of the rest of the orders.

 

Yaku calls when they’re halfway to the old storage warehouse that they pinpointed to be a potential hideout for one of their suspects. They have yet to be able to look inside, to see what equipment might be hiding behind closed doors, and everyone that’s been there has refused to admit them.

 

“Kuroo.” There’s no preamble, no waiting around. Pure urgency seeps into Yaku’s voice, strangling it. “It’s the similar strain to all the previous cases, but the web of it— the magic weaved into this is stronger than I was expecting. I’m working with all the other doctors, but I need— I need you to pick my things up from my office. I don’t have all my notes, and I just— They’re getting worse by the hour.“

 

“Okay,” Tetsurou says. “Okay. Whatever you need. I’ll be there.” He hazards a look to Kenma, who doesn’t look the slightest bit bothered. “One hour. I’ll be there.”

 

He hangs up the phone, and pulls over a minute later, turning to fully face Kenma. He hasn’t gotten a single word out before Kenma’s waving a dismissive hand.

 

“Go take care of whatever it is he needs. I’ll carry on to the warehouse. I’ll call Lev, so I’m not going in alone.” Tetsurou hesitates, and Kenma rolls his eyes. “I’m not going in alone,” he repeats. “It’s _fine._ Yaku-san needs you, and so do those patients. Drop me off at the train and _go.”_

 

And because Tetsurou trusts Kenma, he does.

 

They lead him straight to Yaku when he arrives at the hospital fifty minutes later. He looks worse than Tetsurou’s ever seen him, which he can’t take as anything but a terrible sign. His mind is filled with nothing but thoughts of what they’ll do if they can’t catch anyone, and how Yaku admitted in the smallest voice how scared he was of failing, and putting Japan — and by extension, the rest of the world — at risk of an incurable, magical plague.

 

Tetsurou doesn’t want to fail. Even more, he doesn’t want Yaku to feel that he’s failed.

 

Yaku’s shoulders drop with relief when he sees Tetsurou, and can take all his notes and the sample potions he’s thrown together. There’s no guarantee any of it will work, but there’s no way to know if they don’t try.

 

Kenma’s voice, in the back of his mind: _if you do not enter the tiger’s cave, you will not catch its cub._

 

He assist Yaku off to the side. Hands him the right ingredients, offers a handful of small changes and the statistical data to back his advice. Yaku agrees each time.

 

“It’s okay,” Tetsurou assures him. “You know what you’re doing. Nekomata’s got our whole team out scouring the city. We’re not losing anyone.”

 

If nothing else, they get the patients stabilized for the moment, while Yaku sets in to throw together more complicated potions, and search up stronger spells.

 

Tetsurou has no idea how much time has passed when a text comes in from Yamamoto: they have their guy. They’re bringing him in.

 

He shares the information with Yaku, who looks a little lighter to know it. They’re going to be okay.

 

* * *

 

Yaku stays working for two days straight. Tetsurou only leaves to interrogate their culprits. It takes time to get answers, but he gets them; he’s a good cop, who’s worked hard, and knows the spells and how to use them to get what he needs.

 

Yaku’s the first to get a call, and Tetsurou rushes out all the information he needs for how to remedy the harm done. He’s already on the way to meet him back at the hospital by the time he’s hanging up the phone.

 

They both end up working through the night, but at the end of it all, there’s a new light. Tetsurou takes Yaku back to his apartment, because it’s closer, and they’re both exhausted enough that they barely even make it in the door before they’re crashing, falling right onto the mattress still in stained, rumpled clothes. Tetsurou doesn’t even think to dig out the futon.

 

He wakes up midway through the afternoon to Yaku still snoring, curled up in the middle of the bed. He has one arm thrown across Tetsurou’s middle, and it flops down onto the mattress when Tetsurou rises.

 

It’s a quiet day. He feels lighter than he has in months, knowing things are on their way to being resolved. Knowing Yaku can and will finally sleep a little easier.

 

Tetsurou takes his time to shower and pull on clean clothes, and fixes what he supposes is technically dinner, even if all the food is standard breakfast food. He’s midway through frying eggs when Yaku finally rises, slinking out of the bedroom, hair sticking up in every direction, rubbing at tired eyes.

 

“What day is it?” he asks, voice rough with sleep. He blinks blearily at Tetsurou standing at the stove.

 

“Still Tuesday,” Tetsurou says. “Feel rested?”

 

Yaku scoffs. “I haven’t felt rested in at least eight years.” He stretches his arms above his head, and when he drops them back to his sides again, he softens. “Yeah. Thank you. For— everything.”

 

“Of course,” Tetsurou says. “Of course. Always.” He clears his throat, trying to clear his head of how domestic this feels. The late, slanting sunlight, Yaku’s tired comfort, his cat circling his ankles like she belongs there. “You wanna shower while I finish up? There’re old clothes of Kenma’s in the bottom dresser drawer that should fit alright.”

 

Yaku nods and shuffles out of sight. He comes back fifteen minutes later, looking a little more awake, and a whole lot cleaner. He steps up beside Tetsurou at the counter, peering over his shoulder as he plates their breakfast. He’s wearing Kenma’s sweatpants, but one of Tetsurou’s sweatshirts, and the sleeves hang down to his fingertips. He doesn’t think Yaku would appreciate being called cute, but, well.

 

“This looks good,” he comments.

 

“Is this praise? Are you praising me?” Tetsurou flashes an easy smile to Yaku, who rolls his eyes, already knowing what’s to come. “Oh, Yakkun, I always knew you liked me.”

 

Yaku purses his lips, clearly battling a smile. The smile wins, and he shoves against Tetsurou’s shoulder. “Whatever. You like me just as much, get over yourself.”

 

He walks off to the kitchen table like his words haven’t left Tetsurou’s heart jolting at an unsteady pace. He swallows hard and brings their plates to the table, pausing for a second too long as he tries to decide whether sitting next to or across from Yaku is the lesser of two evils. He sits across from him. Yaku’s legs are stretched out, and his ankles keep knocking against Tetsurou’s. It’s fine.

 

(It’s totally not.)

 

Yaku dries dishes while Tetsurou washes, easy and mindless conversation flowing between them, deciding which documentary they should put on, and whether they ought to start a puzzle or something.

 

It pulls at a wire in his chest.

 

“Set something up,” Yaku tells him, once all the dishes are put away. “I know where you keep your puzzles. Grandpa.”

 

“What’s that make you, then? What’s a reverse cougar?” Tetsurou wants to take back the words as soon as he says them, because they kind of imply _a lot,_ but Yaku laughs in response, a sharp, singular _Ha!_ , and he’s instantly relieved.

 

“Makes me stupid, that’s what,” he calls over his shoulder. They’re probably toeing some sort of line. It feels dangerous. Tetsurou kind of wants to keep pushing, if Yaku’s going to keep letting him.

 

He throws on the first documentary Netflix suggests to him, about ocean life, and settles down on the floor, leaning back against the couch. Yaku sits easy beside him a moment later, dumping the puzzle pieces unceremoniously in front of them.

 

Tetsurou decides twenty minutes into the documentary that he has no idea what’s going on in the slightest, because Yaku’s sitting close enough that their knees are touching, and every time they reach for another puzzle piece, their shoulders and elbows knock together.

 

“I really do need to thank you,” Yaku murmurs after a while. “You seriously . . . It was a lot. What you did. And I’m grateful for it.” He seems particularly interested in a single, all-white puzzle piece, gaze not wavering from it for even a second as he speaks, or as Tetsurou responds.

 

“I should be thanking you. You solved our whole case, on top of saving the country, you know.” He has his full attention on Yaku, puzzle and documentary be damned. “You’re sort of a hero, or something.”

 

Yaku dares to look up at Tetsurou. “Shut up. That’s so lame. You’re so lame.”

 

“Mm. You like it though.”

 

“Whatever.” Yaku rolls his eyes. “So what if I do? What’s it to you?”

 

Tetsurou’s mouth curls into a smile. He leans in the barest amount closer. “You wanna know?”

 

There’s a shift in the air. Yaku turns more towards him. “You gonna tell me?”

 

“I’ll give you something, alright.”

 

He lifts a hand to the back of Yaku’s head, nudging even closer, but stops, just in case Yaku wants to back out of the whole thing. But instead, Yaku closes the last of the gap, hands coming up to cup Tetsurou’s face as he moves their lips together. And it’s—

 

 _Easy._ Everything is easy.

 

This is the tiger’s cave, the tiger’s cub, the tiger. However it is Kenma’s stupid idiom works. All that, for this.

 

It’s worth it. More than worth it.

**Author's Note:**

> this originally....was planned to have a lot more magical elements and a lot more domesticity but, well. here we are. i really really hope you liked this all the same!!!! merry merry christmas riin!!♡♡


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